Industrial surface temperature probes are known, per se, in a number of designs. Common to most of said probes is the fact that the actual temperature sensor element—usually a Pt100 resistor or a thermocouple—is encapsulated in a metal housing in order to prevent damage in tough industrial environments. Additional adapter structures (plates, clamps) are often used in order to allow attachment to a process pipe or vessel. The sensor arrangement thus formed is brought into contact with the process pipe or container at which the temperature is to be measured. The measuring accuracy of such sensor arrangements is strongly influenced by the thermal resistance of the contact between the process pipe or container and the sensor housing or the adapter structure.
Due to technical quality, such as surface roughness and tolerances, the actual body contact on the process pipe is limited to just a few point contacts, for example if two planar, but not perfectly level surfaces contact one another, or in the best case line contacts, for example between a pipe and a plate, the contact surfaces being small in comparison to the overall surface of the sensor element. This leads to a very high heat transmission resistance and thus to long reaction times and significant steady-state deviations between the actual surface temperature and the measured value. In this case, the deviations can certainly exceed 10° C.
It is generally known to reduce the heat transmission resistance between two thermally coupled elements by means of additional thermal bridges which are formed by adapter elements that conduct a heat flow from the vessel laterally to the temperature probe.
Whilst the heat transmission resistance between the adapter element and the vessel can be kept low on account of a large-surface-area design having a plurality of contact points, the heat transmission between the temperature probe and the adapter element is limited due to the small number of contact points resulting from the small dimensions of the temperature probe.
The fact that the temperature probe is required to be replaceable means that a permanent connection which effectively conducts heat, produced for example by welding, soldering or shrinkage, is not an option.
Known structures usually have an extremely high thermal resistance, and yet they also disadvantageously have long reaction times and major steady-state deviations between the actual surface temperature and the measured value. The deviations can exceed 10° C. even for actual surface temperatures of less than 100° C.
The use of thermal interface materials, such as heat-conducting pastes, does not provide many benefits either since the geometry of the contact surfaces does not make it possible to retain such means over a long period of time. The thermal interface materials run off the contact surfaces or dry out over time. This increases the heat transmission resistance between the contact surfaces, and as this resistance increases, so too does the number of measurement errors.
Known semiliquid interface materials are designed for space widths of less than 0.1 mm such that they can reap all the benefits of capillary storage. In order for semiliquid interface materials to have a reasonable service life, the space widths must not exceed 0.5 mm, particularly if the interface enables the semiliquid interface material to flow freely under the effect of gravity. In the industry, however, space widths are rarely kept this narrow.